The basic manual microscope in which an observer examines a specimen through ocular lenses has been available for centuries and is still very much in use. Increasingly, however, automation has been applied to the basic optical microscope and the scanning of slides can now be computer controlled. A typical computer controlled system consists of a microscope, an image sensor (often a video camera) and an image processing computer capable of quantitative measurements of the image, a 3-axis motorized stage, and a stage controller which accepts commands from the computer to move the stage in the X, Y, and Z directions.
Despite this high level of microscope automation, interactive operation, in which the user, rather than the computer manipulates the microscope stage to scan and focus, remains a necessity. It is at times desirable for an operator to use the microscope in "real microscope mode" which is the traditional manner of looking directly through the ocular lens at the image being scanned and focused. It is also sometimes desirable for the operator to use the microscope in "virtual microscope mode" in which the image is collected by the image sensor (e.g. a video camera) and projected on an image display (e.g. TV monitor) and the operator manipulates the stage for image acquisition and analysis.
Presently, when a microscope system is not used in fully automatic computer controlled mode, it can be switched to an interactive stage mode where the stage movement is controlled via a joystick manipulated by the operator. Stage movement in the .+-.X direction is controlled by moving the joystick left and right, movement in the .+-.Y direction is controlled by moving the joystick forward and backward, and movement in the .+-.Z axis direction (for focusing) is achieved by rotating the joystick knob. The speed of stage movement in the X and Y directions is usually proportional to the joystick displacement while the speed of movement in the Z direction is proportional to angular rotation. The joystick is spring-loaded to return to a central null position when released.
There are recognized problems with interactive manipulation of the stage. Cytotechnologists and pathologists who are experienced in the operation of traditional microscopes without motorized stages find the joystick very difficult to use. Scanning a slide involves two simultaneous controlled operations: translation of the slide in the X or Y directions and fine focus adjustment in the Z direction. With a joystick, this involves the simultaneous twisting and rocking of the device with one hand. This cannot be done in a controlled fashion partly because of the complex, non-intuitive nature of the physical movement, and partly because of the speed problem described next. The speed of the stage movement is directly proportional to the amount of joystick displacement, while the amount of stage displacement becomes a function of the speed of joystick displacement and time. This is not intuitive. In addition, regardless of the motor speeds and acceleration ramps, the stage movement tends to be frustratingly slow, or too fast, resulting in overshooting the desired goal. A further problem is that any attempt to move one axis only with a joystick is very difficult because it is a "three in one" control device. Finally, the presence of a mirror in the light path to the ocular reverses the apparent sense of the stage movement: movement of the joystick to the left makes the specimen in the ocular appear to move to the right, and vice versa.
Despite these drawbacks, joysticks do offer the advantages of being ambidextrous, they allow "remote" operation appropriate for "virtual microscope mode", they can be operated with one hand (albeit with difficulty in the usual embodiments) and they may be placed wherever the operator desires and the motors do most of the work.
Unmotorized stages share some problems with the joystick, namely the unmotorized stage has the same apparent direction reversal problem and the effective range of stage sensitivities (i.e. coarse versus fine control ranges) available to both unmotorized stage and joystick, is limited, particularly in X and Y. This is often most noticeable at very low or very high magnification.